Aircraft typically include a plurality of flight control surfaces that, when controllably positioned, guide the movement of the aircraft from one destination to another. The number and type of flight control surfaces included in an aircraft may vary depending, for example, on whether the aircraft is a fixed-wing or rotary-wing aircraft. For example, most fixed-wing aircraft typically include primary flight control surfaces, such as a pair of elevators, a rudder, and a pair of ailerons, to control aircraft movement in the pitch, yaw, and roll axes. Aircraft movement of rotary-wing aircraft in the pitch, yaw, and roll axes is typically controlled by via movement of the rotating aircraft rotors, and may additionally be controlled via movement of one or more flight control surfaces.
The positions of the aircraft flight control surfaces and/or rotors are typically controlled via a flight control system. The flight control system, in response to position commands that originate from either the flight crew or an aircraft autopilot, moves the aircraft flight control surfaces and/or rotors to the commanded positions. In most instances, this movement is effected via actuators that are coupled to the flight control surfaces. Typically, the position commands that originate from the flight crew are supplied via one or more inceptors. For example, many fixed-wing aircraft include a plurality of inceptors, such as yokes or side sticks and rudder pedals, one set each for the pilot and for the co-pilot, and many rotary-wing aircraft include one or more of a cyclic, a collective, and rudder pedals.
In many aircraft, including both fixed-wing aircraft and rotary-wing aircraft, the flight control system may be a hydro-mechanical system, which may include relatively complex hydraulic plumbing and various hydraulic actuators. Although hydraulic actuators are relatively robust, these actuators may not be suitable for all aircraft operating regimes. For example, during quasi-static operations of many fixed-wing aircraft, one or more of the primary flight control surfaces may be held at a generally fixed position, while compensating for the primary flight control surface hinge moments. Such operations can be unsuitable for hydraulic actuators.
More recently, all or portions of the above-mentioned hydro-mechanical flight control systems are being retrofitted or replaced with electromechanical systems. No matter the particular type of system that is implemented (e.g., hydro-mechanical or electromechanical), the flight control system may need to be designed to withstand postulated, though unlikely, component inoperability. For example, the flight control system may need to withstand the postulated occurrence of an actuator becoming inoperable. At the same time, these systems should be designed to prevent a very highly unlikely, yet postulated, common-mode failure that could result in loss of control. Designing flight control systems to meet such design standards can be relatively costly and complex when trying to implement an electromechanical type system.
Hence, there is a need for a fly-by-wire flight control system that can withstand postulated, though unlikely, component inoperability and highly unlikely, yet postulated, common-mode failures, and that can be implemented at a cost that is relatively less costly and/or relatively less complex than presently known systems. The present invention addresses at least this need.